Our goal is to characterize active ion transport by the isolated Lepidopteran midgut and to define its role in epithelial function during development. We will use cytology, biophysics, and biochemistry to describe, characterize, and isolate the transport mechanism and then to reconstitute it from its component parts. Our aims for the proposed study are (0) to perfect a new glass midgut chamber with replaceable apertures (1) to publish the morphology and fine structure of the anterior, middle, and posterior regions of the midgut (2) to study biophysical properties of each region separately (3) to investigate cell degeneration associated with the decay of the transport system and with the loss of the potassium pump in development (4) to investigate whether the delta-endotoxin from Bacillus thuringiensis acts primarily as an uncoupler of oxidative phosphorylation or as a stimulant of the backflux of potassium through the pump (5) to determine the concentration of profiles of potassium on the transporting and non transporting midgut and made a definitive identification of the transporting cell and pump location (6) to isolate membrane vesicles and to purify a plasma membrane ATPase as initial steps in the isolation and reconstitution of th alkali ion transport system and (7) to review active cation transport by insects. the structural study will employ standard transmission electron microscopy, histochemistry and such surgical methods as the transplantation of tissues. Biophysical techniques will include the measurement of the PD, the short circuit current, the epithelial and cellular resistances, tracer-labeled ionic fluxes, and pool sizes from tracer influx kinetics. To investigate its mode of action we will use stable, potent, 33,000 dalton fractions of the delta-endotoxin from B. thuriniensis var alesti. The concentration profiles will be obtained by electron probe X-ray microanalysis on frozen-hydrated sections. Biochemical methods will include differential and density gradient centrifugation, macroporous gel filtration, and ion exchange chromatography. Reconstitution of the system will be attempted on both spherical and planar bilayer lipid membranes.